why do we twitch when we sleep

A hypnagogic jerk is an involuntary muscle spasm that occurs as a person is drifting off to sleep. The phenomenon is so named in reference to the hypnagogic state the transitional period between wakefulness and. Hypnagogic jerks, are also commonly known as hypnic jerks or sleep starts. The muscle spasms may occur spontaneously or may be induced by sound, light or other external stimuli. Some people report hypnic jerks accompanied by hallucinations, dreams, the sensation of falling, or bright lights or loud noises coming from inside the head. [ Sleep starts are quite common, with some research suggesting that 60 to 70 percent of people experience them. Many individuals may be visited by nightly hypnic jerks without even knowing it, as the twitches often go unremembered, particularly if they don t cause a person to wake up. Some scientists believe certain factors, such as stress, anxiety, fatigue, caffeine and , may increase the frequency or severity of hypnic jerks, but conclusive research is lacking on the subject. Intense physical activity or exercise in the evening may also contribute to increased hypnic jerks, said Michelle Drerup, a psychologist and behavioral sleep medicine specialist at the Cleveland Clinic s Sleep Disorders Center in Ohio. Researchers are also unsure why hypnic jerks occur, but a few theories exist. One hypothesis says that hypnic jerks are a natural part of the body s transition from alertness to sleep, and occur when nerves misfire during the process.

Another popular idea takes a more evolutionary approach to hypnic jerks, explaining that the spasms are an to the relaxation of muscles during the onset of sleep the brain essentially misinterprets the relaxation as a sign that the sleeping primate is falling out of a tree, and causes the muscles to quickly react. More often than not, hypnic jerks are completely normal and nothing to be concerned about, Drerup told Live Science. However, if the jerks themselves, or the anxiety you experience about having them, are, you should talk to a sleep specialist about your concerns. This article was originally published in 2013. Additional reporting by Senior Writer Laura Geggel. Original article on. As we give up our bodies to sleep, sudden twitches escape our brains, causing our arms and legs to jerk. Some people are startled by them, others are embarrassed. Me, I am fascinated by these twitches, known as. Nobody knows for sure what causes them, but to me they represent the side effects of a hidden battle for control in the brain that happens each night on the cusp between wakefulness and dreams. Normally we are paralysed while we sleep. Even during the most vivid dreams our muscles stay relaxed and still, showing little sign of our internal excitement. Events in the outside world usually get ignored: not that I d recommend doing this but experiments have shown that even if you sleep with your eyes taped open and someone flashes a light at you it is.

But the door between the dreamer and the outside world is not completely closed. Two kinds of movements escape the dreaming brain, and they each have a different story to tell. Brain battle The most common movements we make while asleep are rapid eye-movements. When we dream, our eyes move according to what we are dreaming about. If, for example, we dream we are watching a game of tennis our eyes will move from left to right with each volley. These movements generated in the dream world escape from normal sleep paralysis and leak into the real world. Seeing a sleeping persons' eyes move is the strongest sign that they are dreaming. Hypnic jerks aren't like this. They are most common in children, when and they do not reflect what is happening in the dream world - if you dream of riding a bike you do not move your legs in circles. Instead, hypnic jerks seem to be a sign that the motor system can still exert some control over the body as sleep paralysis begins to take over. Rather than having a single sleep-wake switch in the brain for controlling our sleep (i. e. ON at night, OFF during the day), we have two opposing systems balanced against each other that go through a daily dance, where each has to. Deep in the brain, below the cortex (the most evolved part of the human brain) lies one of them: a network of nerve cells called the reticular activating system.

This is nestled among the parts of the brain that govern basic physiological processes, such as breathing. When the reticular activating system is in full force we feel alert and restless - that is, we are awake. Opposing this system is the ventrolateral preoptic nucleus: 'ventrolateral' means it is on the underside and towards the edge in the brain, 'preoptic' means it is just before the point where the nerves from the eyes cross. We call it the VLPO. The VLPO drives sleepiness, and its location near the optic nerve is presumably so that it can collect information about the beginning and end of daylight hours, and so influence our sleep cycles. As the mind gives in to its normal task of interpreting the external world, and starts to generate its own entertainment, the struggle between the reticular activating system and VLPO tilts in favour of the latter. Sleep paralysis sets in. What happens next is not fully clear, but it seems that part of the story is that the struggle for control of the motor system is not quite over yet. Few battles are won completely in a single moment. As sleep paralysis sets in remaining daytime energy kindles and bursts out in seemingly random movements. In other words, hypnic jerks are the last gasps of normal daytime motor control. Some people report that hypnic jerks happen as they dream they are falling or tripping up.

This is an example of the rare phenomenon known as, where something external, such as an alarm clock, is built into your dreams. When this does happen, it illustrates our mind's amazing capacity to generate plausible stories. In dreams, the planning and foresight areas of the brain are suppressed, allowing the mind to react creatively to wherever it wanders - much like a responds to fellow musicians to inspire what they play. As hypnic jerks escape during the struggle between wake and sleep, the mind is undergoing its own transition. In the waking world we must make sense of external events. In dreams the mind tries to make sense of its own activity, resulting in dreams. Whilst a veil is drawn over most of the external world as we fall asleep, hypnic jerks are obviously close enough to home - being movements of our own bodies - to attract the attention of sleeping consciousness. Along with the hallucinated night-time world they get incorporated into our dreams. So there is a pleasing symmetry between the two kinds of movements we make when asleep. Rapid eye movements are the traces of dreams that can be seen in the waking world. Hypnic jerks seem to be the traces of waking life that intrude on the dream world. If you would like to comment on this video or anything else you have seen on Future, head over to our or message us on.